Telegraphic receiver



May 3, 94 E. OTTENBERGER ET AL 2,241,885

TELEGRAPHI C RECEIVER Filed OCT.. 26, 1939 Patented May 13, 1941 airco s'rrs TELEGRAPHIC RECEEVER gesellschaft, company Berlin-Tempelhof, Germany,

Application (ictober 26, 1939, Serial No. 301,318 In Germany October 27, 1938 (Cl. Z50-20) 3 Claims.

The invention relates to telegraphic receivers of the kind having means for the compensation of fading effects, and it consists in certain features of novelty which will appear from the following description, reference being had to the accompanying drawing, in which Fig. 1 is a diagram showing a known arrangement, Fig. 2 is a diagram representing one embodiment of the invention, Fig. 3 is a diagram showing a modification of the arrangement represented in Fig. 2.

Receivers of the said kind have a telegraph heterodyne in the manner illustrated in Fig. 1. An amplifying tube here supplies the amplifying signalling frequency fl to a regulating diode 4 over a high frequency transformer 2, 3. The regulating voltage for the electron tubes connected at Q is produced at resistance 5 by the rectied diode current. Part of the signalling frequency is supplied to a rectifying tube 'I over a coupling condenser 6. In the case of telegraphy worln'ng, the heterodyne frequency f2 is conveyed to the grid g of tube 1.

This arrangement has a fundamental disadvantage. In fact, as the secondary 3 of the high frequency transformer is coupled to the heterodyne circuit by condensers 6, M, part of the voltage f2 is impressed upon diode 4, this diode hence producing an additional regulating current by which an undesirable drop of poten- 'l tial isy caused to arise. As a result the amplification of theregulated tubes will be controlled downward without the signalling frequency acting upon the receiver.

In accordance with the invention the arrangement is such that the heterodyne circuit shall not affect the circuit concerned with the fading regulation. To such end the heterodyne is coupled with the aid of a differential winding.

In Figs. 2 and 3 such differential winding is designated 9, I0, The outer and interelectrode capacities of the second rectifying tube 1, Fig. 2, is balanced by a condenser I I. This condenser is so dimensioned and adjusted that the magnetic field originated. by current JI in the winding 9 shall be just compensated by the magnetic field produced in winding I by current J2. Consequently, no heterodyne voltage is induced in winding 3, whereby the diode 4 shall not generate a regulating voltage in addition to that effective in the case of telegraphy working.

The representation adopted in Fig. 3 is simplified with respect to Fig. 2, being of the type designated as equivalent circuit. Amplifying tube I and coil 2 represent the signalling-frequency circuit while diode 4 and coil 3 represent the regulating circuit. The heterodyne voltage f2 is supplied to the differential winding 9, I0. Cglc denotes a condenser which represents the outer and interelectrode capacities of tube 1. These capacities are balanced by condenser II. A phase-pure compensation may be obtained by means of a resistance I3 connected in parallel with condenser I I and arranged to balance the grid leak resistance I 2. In most cases however it will be sufficient to compensate in amplitude fashion.

The diode circuit may of course be connected by still other means than those here dis-closed.

In order to insure a perfect compensation the invention further proposes to minimize the capacitive coupling between the windings 9, I0 on the one hand and Winding 3 on the other hand, such coupling effect being due to the leakage capacities of these windings. For this purpose the winding 2 is located between winding 3 and the windings 9, I3, a static screening being obtained in this way.

What is claimed is:

1. In a telegraphic receiver having a rectifying tube, a heterodyne oscillator, means for applying received signal oscillations from said oscillator to said rectifying tube to produce beat frequency signals and a gain regulating circuit for controlling the gain of the receiver in accordance with received signal levels, means for preventing the heterodyne voltage from infiuencing said regulating circuit, comprising a primary winding, a first secondary winding coupled with said primary winding for applying received signals to said rectifier, a second secondary winding for applying said received signals to said gain regulating circuit, and a connection from said heterodyne oscillator to the mid-point of said first secondary winding to differentially cornpensate said heterodyne oscillation in said second secondary winding.

2. A receiver according to claim 1, wherein said primary winding is arranged between said first and second secondary windings to minimize capacitive coupling between said secondary windmgs.

3. A receiver according to claim 1, further comprising a condenser in circuit with said first secondary winding to balance the outer end interelectrode capacities of said rectifier tube.

ERI-IARD OITENBERGER. HERBERT PHMEYER. 

